Alan's Workbench

[Mayner]

Mike Sharman explained seems to have introduced the concept of square cuts outs in the frames in conjunction with what he termed "Sub Hornblocks" in his "Flexchas" booklet 1st published 1982. Written from a scratchbuilding perspective writed about machining V groved axle brushes to slide in the subhornblocks and filing up & individually matching the subhornblock and brush. 

While Mike Sharman did not specify frame cut out or hornblock sizes he noted "allow Brushes to move approx 1mm above and below axle centre line"

The square frame cut out and individual hornblock is similar in concept from prototype practice.

My first compensated loco assembled 84-5 was a TMD Midland tank the original TMD (brass chassis) had rectangular frame cut outs suitable for use with a compensated frame bush (I used Sharman), my second a scratchbuilt 0-6-0 with "Perseverence" etched hornblocks and compensated brushes (I was not happy with the 0-6-0 and scrapped/dismantled the loco about 30 years ago, hopefully I will get round to building a replacement!)

I usually assemble my compensated locos with all driving axles running in hornblocks (including fixed axle) as I like to treat the wheelsets as separate sub assemblies for painting/maintenance.  I try and ensure that the upper edge of the floating (sub) hornblocks are level and usually mount the fixed hornblock 1mm lower & eliminate vertical travel by mounting the keeper wire higher.

I usually assemble chassis on a flat surface (hardboard or MDF) with a piece of rectangular stripwood to ensure angles are at 90°, I have always found a coupling rod jig similar in principal to the "London Road" jig in Alan's photo perfectly adequately, one of the most improtant factors in assembling a compensated chassis is to ensure that the hornblocks are truly vertical before soldering in place, otherwise a chassis will bind when the floating axles move up and down.

 

 

 

[Tullygrainey]

All you've ever wanted to know about building chassis but were afraid to ask...

[Tullygrainey]

33 minutes ago, Mayner said:

one of the most improtant factors in assembling a compensated chassis is to ensure that the hornblocks are truly vertical before soldering in place, otherwise a chassis will bind when the floating axles move up and down.

Very important. A lesson I learned the hard way!